Witnesses told CNN affiliate KRNV
in Reno they could see buildings shake following the explosion.
The air ambulance company American Medflight
released a statement late Friday saying three crew members and a patient had died.
"We are devastated by this event and wish we had answers to the many questions being asked at this time," the statement said. "We are cooperating fully with the National Transportation Safety Board and the Federal Aviation Administration as they investigate the accident."
It is at least the third air ambulance crash in recent months
. In July, a Piper Cheyenne carrying three crew members and one patient crashed in Northern California, killing all on board. The plane, which was part of Cal-Ore Life Flight's fleet, was headed to Oakland International Airport to the south.
In March, a medical helicopter crashed
in a wooded area of Coffee County, Alabama, killing all four on board, including a patient being airlifted after a car crash.
In Friday's crash,
cardiologist Rodney Badger told the Elko Daily Free Press
the plane had just taken off from Elko Regional Airport with a heart patient who was being transported to the University of Utah.
Allen Kenitzer of the FAA Office of Communications said the cause of the Piper PA 31 aircraft crash was unknown and there were no known injuries on the ground, KRNV reported.
Multiple explosions resulted from the crash into the parking lot of the Barrick Gold Corp. near the Elko airport, and flames were visible near a casino, motel and senior housing complex, the Elko newspaper reported.
"Our priority at this time is to look after the well-being of the affected family members and their co-workers and to be responsive to their needs," American Medflight's statement said. "We ask the media and interested parties to be patient with the investigation process and honor the privacy of the family and friends of those who have lost their lives."